The antennas of mobile communication devices are typically designed to have a VSWR (Voltage Standing Wave Ratio) of 3 or less in free space. The VSWR is a measure for the reflected RF energy. Environmental influences, e.g., a user's hand or a user's head in the vicinity of the mobile device, in general cause a degradation of the antenna performance, i.e., an increase of the VSWR. Adaptive antenna modules shall counteract this degradation and maintain or regain a low VSWR.
From the European patent application EP 0685936 A2, an adaptive antenna matching circuit is known. The circuit comprises a matching network and a coupler, both being electrically connected to a signal path. The circuit further comprises a processor that is electrically connected to the matching network and to the coupler. The matching network comprises tunable reactance elements which are electrically connected in series to the signal path or which electrically connect the signal path with ground. The process of matching the impedance of the signal path comprises several steps of tuning single variable reactance elements individually and on after another and storing preferred settings within a memory. Thus, the process of matching the impedance is complicated, power consuming and demands for a complex and costly processor circuit.